Method of producing shaped bodies from powdered metals



May 31, 1960 A. BLAINEY 2,938,791

METHOD OF PRODUCING SHAPED BODIES FROM PQWDERED METALS Filed May 26,1949 Fig.3.

O- N 1' o a m o n In R3 m Inventor y/VLflN BMIAIEX.

g Attorney RMR M METHOD OF PRUDUCING SHAPED BODIES FRO POWDEREZ) METALSAlan Blainey, London, England, assignor, by mesne assignments, to theUnited States of America as represented by the United States AtomicEnergy Commission Filed May 26, 1949, Ser. No. 95,427

2 Claims. (Cl. 75-226) This invention relates to the production ofshaped bodies by compacting pulverulent materials in a mould or die.

In the forming of shaped bodies by compaction of powders in a die,frictional effects, particularly between the powder and die walls, causea falling off in compacting pressure as the distance from the movablecompression members of the die increases. Hence, to ensure that suchshaped bodies are satisfactorily compacted throughout, it has beennecessary to limit the ratio of the dimension of the compact in thedirection of the compression (herein referred to as the depth of thebody) to the transverse dimension, and accordingly bodies havingsections of small thickness and substantial depth have not beenpractical. The above mentioned frictional effects have also made itdifficult, if not impracticable, to obtain in shaped bodies of compactedpowders satisfactory reproduction of relatively deep patterns orimpressions carried by the wall of the die.

The object of the present invention is to provide a method of formingshaped bodies of co'mpacted powder whereby satisfactory compaction ofthe material is obtained in relatively thin sections of substantialdepth, and whereby the compression may serve to apply a pattern,impression or the like to the transverse surface of the body.

In accordance with the invention in the production of shaped bodies bycompacting powder masses, substantially uniform compaction of powder insections of substantial depth and relatively small thickness is obtainedby compacting the powder mass with such sections in contact with a massof substance which under the conditions of compaction has the quality ofdeforming or flowing and so transmitting isotropic pressure.

Also in accordance with the invention, shaped bo'dies having sections ofrelatively small thickness and substantial depth are produced frompowders by subjecting the powder forming the said sections to pressurethrough ,the medium .of a mass of substance which is subjected tocompression with the powder and has the quality of deforming or flowingunder the conditions of compaction and so transmitting isotropicpressure.

Also according to the invention a shaped body is formed by compacting amass of powder material in a die within a surround or about a core orcores of a substance, which under the conditions of compacting has thequality of so flowing or deforming as thereby to transmit isotropicpressure. The powders may be fine or coarse for use in the invention andthe resulting compacted powder, while preferably impermeable, may bemade porous, if desired.

The substance forming the core employed according to the invention maybe one which will flow at o'rdinary temperatures when subjected to thecompacting pressure, for example metallic sodium, lead or other softmetal or soft metal alloy, or it may be a substance which will flowunder such pressure at an elevated temperature at which the compressionwill be effected, for example a metal or alloy which softens at atemperature which conveniently may be in the neighbourhood of thesintering or softening temperature of the powdered material. The coremay alternatively be of a plastic or resilient sub stance, for examplerubber or a rubber-like polymerisation product (for example, silicone,rubber, polyvinyl chloride or the like) or a thermoplastic substance.

By means of the invention a core or cores of metal or alloy may beencased in a sheath of compacted powdered metal or heavy metal carbide,oxide, or alloy by compressing the powdered metal or metal carbide oroxide or alloy about the core or cores in an appropriate die at atemperature at which the core or cores soften and the surrounding powderwill sinter or cohere.

In carrying the invention into effect according to a preferred method,as applied to forming a protective sheath of beryllium metal on a bar ofuranium metal, a demountable die, preferably of a metal of small creepat 800 C., for example Mond nickel-chromium alloy Nimonic ornickel-titanium carbide, is used, the die having a cavity which willreceive the bar leaving a space between sides and ends of the bar anddie walls equal to about twice the desired thickness of the sheath. Aquantity of powdered beryllium, which has preferably een ground in thepresence of a hydrocarbon oil, is spread uniformly over the face of thelower compression member of the die .to a thickness corresponding to theclearance between the uranium bar and the die walls. The uranium bar iscentrally placed on the layer of beryllium and further beryllium powderadded to fill the spaces between the bar and the die wall and for alayer over the bar of substantially the'sarne depth as the initiallayer. The beryllium powder mass is then thoroughly impregnated with ahydrocarbonoil to displace air. The upper compression member of the dieis brought into position and the charge subjected to a pressure ofsubstantially 10 tons per square inch while the die and contents areheated to a temperature above the 5- transition point of uranium,preferably at about 800 C., by electric heating elements associated withthe die or by passage of current through the charge and core by wayofthe die compression members.

At the temperature specified uranium is very soft and under the actionof the pressure applied will spread laterally in the die exertingpressure perpendicularly on the powdered beryllium forming the sidewalls of the sheath, which powdered beryllium will be compacted into animpervious mass about the uranium. The die compression members may beprovided with grooves or slots on their faces so as to form ribs,ridges, fins or the like on the sheath. When the compacting action iscomplete, the die is cooled and taken apart for the removal of the hethe u ani m ba A ran um ba sheathed with zi co ium may be made in asimilar way'using zirconium powder in place of beryllium powder.

The atmosphere provided by vaporisation of the hydrocarbon preventsatmospheric attack of the metals.

According to a further form of the invention, powdered metal, forexample beryllium, zirconium, molybdenum, tungsten titanium, tantalum,niobium, iron, copper, brass, bronze and light metal alloys iscompressed at ordinary temperatures to form shaped bodies havingprotuberances, threads, corrugations or the like surface effects on thelateral wall (i.e. the wall which extends in the direction of theapplied pressure) by employing a split or demountable die having theappropriate surface effects and making use of a plastic or resilientcore or cores. Thus a cylindrical body carrying an external thread maybe produced by filling powdered metal around a cylindrical core in asplit cylindrical die carrying the thread counterpart, the filling beingeffected as described above.

Compacting pressure is then applied to give a preform,

which after removal from the die may be subjected to sintering treatmentin the usual way. The core may be formed of resilient or elasticmaterial, such as rubber, or of sodium, lead or other soft metal or softmetal alloy which is melted out prior to sintering.

By employing a plurality of separate core members of a substance capableof transmitting isotropic pressure under the conditions of thecompacting operation, compacts having narrow internal channels may beproduced by the method of the invention. In that way such shaped bodiesas gas turbine blades having internal cooling channels may be produced.

If the substance capable of transmitting isotropic pressure is in theform of a surround it may be employed to compact metal or other powderabout a shaped mandrel. The surround in this case may be an annular masshaving an internal pattern, shape or form suitable for producing acompact having, for example, high fins or other protuberances.

The accompanying drawings illustrate ways of carrying the invention intoeffect.

Fig. 1 is a diagrammatic view of apparatus for preparing bodies of theinvention.

Fig. 2 is a cylindrical sheathed rod, partly in section.

Fig. 3 is a body having an external screw thread.

Fig. 4 is a cross section of a body having a sheath carryingcorrugations.

Fig. 5 is an elevation partly in section of the body shown in Fig. 4.

Referring to Fig. 1, the platens 2 of a press or other member to whichpressure or impact may be applied are separated by insulating members 9from the metal plates 14 carrying the compression members 3 of ademountable die 1, supported on block 8. The die 1 may be of Nimonic ornickel-titanium carbide. Within the die body is contained beryllium ortitanium or other metal powder 7 and a cylindrical core 15, which may beof soft metal, or where beryllium or titanium are used, may be uraniumas described above. The die may be heated by means of the electricalheating element represented by 23, the ends 24 and 25 of which areconnected to a suitable source of current supply.

Where the die walls are of sufficiently low conductivity, heating'of thedie contents may be effected by passage of current through the diecontents, current being passed to and from the compression members 3 bycables 6. In

this case the compression members 3 may be of metal of good electricalconductivity, e.g. copper, and may be tippedwith discs of material oflower conductivity, e.g. copper-tungsten alloy, so that the end faces ofthe compacted powder are not unduly cooled by contact with thecompression members. l

The die is filled with powder and a suitable core as described above andheat and pressure are applied to compact the powder 7 to form animpervious sheath about the core 15. Fig. 1 illustrates the apparatus atthe conclusion of the compacting treatment, and Fig. 2 shows '4 thesheathed bar after removal from the demountable die. The bar 15 carriesa sheath 7a of compacted metal powder.

By providing the inner surface of the die members with a thread, a bodyas shown in Fig. 3 may be produced. The inner space 15a was occupied bya sodium, lead, lead-tin or other low melting point alloy core aroundwhich was compacted metal powder in an internally threaded demountabledie. The core was then removed through an opening bored in the end faceand the resulting hollow 17 body sintered in the ordinary way.

. To produce the body shown in Figs. 3 and 4 a de mountable die havinginternal corrugations is employed, the core 15 of uranium, for examplebeing provided with a sheath 25 of corrugated surface in the mannerdescribed above.

I claim:

1. A method of producing a shaped body constituted by a core of uraniummetal completely enveloped in a sheath of compacted beryllium powder,which method comprises the steps of placing the uranium core on a. layerof uncompacted powder beryllium, surrounding the core with the powderand covering it with a further layer of uncompacted powder beryllium,applying compacting pressure of approximately 10 tons per square inch tothe said layers to compact the whole while heating the whole to atemperature above the 18- transition point of uranium, whereby theuranium but below the melting point thereof will flow and transmitisotropic pressure to compact'the powder beryllium surrounding the core.

' 2. A method of producing a shaped body constituted by a core ofuranium metal completely enveloped in a sheath of compacted zirconiumpowder, which method comprises the steps .of placing the uranium core ona layer of uncompacted zirconium powder, surrounding the core withzirconium powder and covering the core with a further layer ofuncompacted zirconium powder, applying compacting pressure ofapproximately 10 tons per square inch to the said layers to compact thewhole while heating the whole to a temperature above the 8- transitionpoint of uranium but below the melting point thereof, whereby theuranium will flow and transmit isotropic pressure to compact thezirconium powder surrounding the core.

References Cited in the file of this patent UNITED STATES PATENTS

1. A METHOD OF PRODUCING A SHAPED BODY CONSTITUTED BY A CORE OF URANIUMMETAL COMPLETELY ENVELOPED IN A SHEATH OF COMPACTED BERYLLIUM POWDER,WHICH METHOD COMPRISES THE STEPS OF PLACING THE URANIUM CORE ON A LAYEROF UNCOMPACTED POWDER BERYLLIUM, SURROUNDING THE CORE WITH THE POWDERAND COVERING IT WITH A FURTHER LAYER OF UNCOMPACTED POWDER BERYLLIUM,APPLYING COMPACTING PRESSURE OF APPROXIMATELY 10 TONS PER SQUARE INCH TOTHE SAID LAYERS TO COMPACT THE WHOLE WHILE HEATING THE WHOLE TO ATEMPERATURE ABOUT THE B-R TRANSITION POINT OF URANIUM, WHEREBY THEURANIUM BUT BELOW THE MELTING POINT THEREOF WILL FLOW AND TRANSMITISOTROPIC PRESSURE TO COMPACT THE POWER BERYLLIUM SURROUNDING THE CORE.